The linear stage:

Dimensions: 35x35x13 mm

Translational range: ±4 mm

Precision: M3 screws has a pitch of 0.5 mm, so 1/8th of a turn corresponds to 0.0625 mm of translation.

Parts:

• 40mm M3 screw
• 4 M3 hexnuts
• One bicycle spoke
• Two springs from ballpoint pens

Print the top and bottom parts. Melt the two inner hexnuts into the plastic:

Cut the two springs in half (or other suitable size). Cut the bike spoke (so it's sharp) and assemble everything.

The linear stage shouldn't exhibit any free play.

OpenSCAD files

2. The square kinematic mirror mount

Mirror dimensions are 18x26mm

Download the file.

Additional components are:

• 1 steel ball bearing (Ø = 4mm)
• 2 tension springs ()
• 2 M3 dome nuts
• 4 M2 screws (or possibly M1.5 - I don't remember)
• 2 M3 12mm screws, 4 M3 hexnuts
• 1 paper clip (to attach the springs)

Print the 3 parts and assemble. It should look like this: